I don't understand - instance variables are perfect for things like health. They are kept independently for each instance, and an event like "If health < 0, destroy sprite" will individually destroy sprites which run out of health, and never affect all of them at once.
Are you sure there isn't a mistake in the tutorial, or a mistake in your events?
That's it what I tried to say boss:
o, if you create a new enemy, the engine will treat this enemy as a unique object (UID and IID), but you can know where it is and manipulate him by making a conditional meeting your necessity, so, when the bullet hit the monster, that specific monster, inside that conditional, will lose health or die. ^^
I mean this is a treat when you have, for example, a rocket with smoke, where the smoke is attached to the rocket.
To explain this topic, you can set individual instance variables for each smoke and each rocket, when creating them. Mean "instances" as "index numbers stored as variables".
When the rocket is destroyed, make sure to destroy the smoke with the same index number as the destroyed rocket.
How to set instances: Instances CAPX
Live sample: Instances HTML5
And all without UID and IID, you really don't need to care about them. They are very much volatile ^^